X-ray lithography is a technology which is competing with photolithography in the manufacture of semiconductor devices. X-ray lithography enables the formation of minute patterns on the order of sub-micron levels by utilizing rays of a shorter wavelength than the ultra violet rays which are used in photolithography. These rays of a shorter wavelength, x-rays, are subject to less diffraction and therefore can be used to produce much finer features on semiconductor devices. The ability to produce much finer features using x-rays allows the creation of denser circuitry than was previously possible with photolithography. A description of fundamental x-ray lithography techniques is given in U.S. Pat. No. 3,743,842, the contents of which are hereby incorporated by reference.
In furthering the x-ray lithography technology, suitable membranes for the fabrication of x-ray masks are required. These membranes are a critical element in applying x-ray lithography.
U.S. Pat. No. 4,866,746 discloses an x-ray mask membrane material made of boron nitride and silicon nitride in a composition range which results in optimum hardness and toughness.
U.S Pat. No. 4,152,601 discloses a membrane material consisting of multiple layers of silicon nitride and silicon oxide.
U.S. Pat. No. 4,804,600 discloses an x-ray lithography mask made on an organic plastic film and then transferred and bonded to a support. The support has a groove which facilitates the flow of adhesive and the patent is directed to the transfer process and the advantages of the groove.
U.S. Pat. No. 4,940,841 discloses a membrane for use in an x-ray mask which comprises boron, silicon and nitrogen in a preferred composition range and made under specific preparation conditions.
U.S. Pat. No. 4,647,517 discloses a mask for x-ray lithography which uses epitaxially grown membranes of silicon doped with boron and germanium. The epitaxial membrane film is grown by conventional methods, i.e. at high temperature (at or above 1,000.degree. C.), and on one side of the wafer only. The process is limited in the range of boron and germanium concentrations, allowing concentrations of boron up to only 2.times.10.sup.20 atoms/cm.sup.3 (approximately 1 atom of boron per 250 atoms of silicon) and of germanium up to only 5.times.10.sup.20 atoms/cm.sup.3 (approximately 1 atom of germanium per 100 atoms of silicon).
None of these references discloses a membrane material suitable for x-ray lithography comprising silicon doped with boron and/or germanium in high concentrations and prepared at low temperature. Such high dopant concentrations and preparation at low temperatures allows greater control of the membrane tensile and compressive stress, resulting in superior membranes.
A genuine need thus exists in the art for a membrane material which can be doped with boron and/or germanium in high concentrations.